Xenon flash lamps for testing solar cells are known. The use of xenon flash lamps has the disadvantage that a poor reproducibility of rapidly cyclic measurements arises since a capacitor charge influences a flash power. Moreover, the xenon flash lamps have only a short lamp lifetime in conjunction with high process costs and a high use of energy. Furthermore, the emitted spectrum is fixedly predetermined and cannot be tracked. Moreover, a high power is consumed in wavelength ranges in which solar cells are not active.